The present invention is directed to dental and orthodontic articles, and more particularly to such articles made from alloys of reactive metals.
Traditionally, systems used for the orthodontic movement of teeth consist of an archwire that is deformed and bent into a shape so as to provide a load or force on one or more orthodontic brackets attached to the patient""s teeth to move the teeth in a predetermined direction. Various materials and alloys are known for use in such orthodontic archwires, as well as for the brackets themselves. These known materials include stainless steels, shape memory and/or superelastic nickel titanium alloys, ceramics, and materials with organic and metallic components, among others, all of which have vastly differing properties. The specific material selected depends on the orthodontic purpose for which the device is to be used. The most widely used materials, based on their functionality as opposed to their aesthetic properties, are metallic alloys. Within the realm of available alloys, the selection of a particular alloy for use in an orthodontic or dental treatment is influenced by a variety of factors, including: (1) the wire strength and stiffness, which determine the amount of forces available for tooth movement; (2) the working range of the wire, which determines the amount of tooth movement that can be obtained before the wire comes to rest in a deformed state; (3) the ease with which the wire can be bent and manipulated; and (4) other physical and mechanical characteristics of the wire, such as transformation temperature, etc.
In addition to the foregoing parameters, it must be borne in mind that orthodontic treatments are generally accomplished in several stages, each of which may require a different type of wire or a wire possessing different properties. In the initial stage of treatment, leveling and alignment of the teeth takes place. In this stage, highly flexible wires are required which exert low forces over long working ranges. Suitable alloys for such archwires are NiTi-based alloys. In the intermediate stage of treatment, leveling and alignment of the arches are generally completed and minor adjustments in the tooth relationships, as well as the overall arch relationship must be addressed. At this stage of treatment, wire properties and characteristics required include high stiffness, moderate working ranges, relatively easy bendability and low coefficient of friction. Beta III titanium alloys and stainless steels are frequently used. These wires, however, do not typically possess all the desired properties and characteristics, although they are currently some of the most suitable materials that are commercially available. During the final or xe2x80x9cfinishingxe2x80x9d stage of treatment, either a soft wire is used for settling and minor adjustments of teeth, or a very stiff wire is used for locking the teeth in their intended ideal position, depending on the specific treatment. Soft stainless steel such as braided wires or very hard stainless steels or other alloys such as Co/Cr based alloys are generally used in these contexts, respectively.
Beta phase titanium alloys provide many of the desired characteristics required during the second stage of treatment, including intermediate stiffness, working range and bendability. On the other hand, NiTi based alloys exhibit an improved working range vis-a-vis beta phase titanium alloys, however, they have relatively low stiffness.
What are needed are dental and orthodontic articles, including adhesives, comprised of alloys which possesses a broad range of the properties desired in orthodontic treatments, extending through the initial, intermediate and final stages of treatment.
In its broadest aspects, the present invention is directed to dental and orthodontic articles which comprise an alloy having as a primary constituent at least one element selected from the group consisting of Ti, Zr, Si, Mo, Co, Nb and Be. The alloy may further include at least one secondary alloying element selected from the group consisting of Ta, Cr, Al, V, Pd, Hf and Fe. Alloys made from these materials, which are reactive elements, possess unique properties, including improved flexibility, combined with moderate stiffness. The combination of increased flexibility and moderate stiffness is believed to be highly desirable for dental and orthodontic articles such as orthodontic wires, springs, brackets and endodontic and dental files or reamers.
In a preferred embodiment, a dental or orthodontic article comprised of an alloy of reactive metals has a modulus of elasticity in the range of about 5 million to 15 million psi and has a maximum average grain size of about 100 microns. Even more preferably, the primary constituent of the alloy is titanium or zirconium, and it is also preferred that the primary constituents are a combination of titanium and zirconium. Alloys and the articles produced therefrom, are biocompatible, and the alloys exhibit at least partial superelastic and shape memory characteristics.
In order to achieve the desired stiffness levels, it is believed that the alloys of this invention require a significant amount of cold work when formed into a wire shape. This will also affect the grain size which can have a significant impact on the material properties, particularly wires wherein finer grain structures tend to produce greater flexibility and fatigue resistance. Furthermore grain size becomes particularly important when the material exhibits any degree of shape memory and/or superelastic behavior.